KR101910988B1 - Binder composition for secondary cell negative electrode, slurry composition for secondary cell negative electrode, negative electrode for secondary cell, and secondary cell - Google Patents

Abstract

assignment
A binder composition having high adhesion between a current collector and an electrode active material layer after charging / discharging, and particularly contributing to improvement in cycle characteristics and low-temperature output characteristics at a high temperature of a secondary battery.
Solution
The binder composition according to the present invention contains a binder and a propargyl group-containing compound, and the content of the propargyl group-containing compound is 0.1 to 20 parts by mass based on 100 parts by mass of the binder.

Description

TECHNICAL FIELD The present invention relates to a binder composition for a secondary battery negative electrode, a slurry composition for a secondary battery negative electrode, a negative electrode for a secondary battery, and a secondary battery. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a negative electrode composition,

The present invention relates to a binder composition for a secondary battery negative electrode (negative electrode), and more particularly to a binder composition for a lithium ion secondary battery negative electrode. The present invention also relates to a slurry composition, a negative electrode and a secondary battery using such a binder for a secondary battery negative electrode.

2. Description of the Related Art In recent years, portable terminals such as a notebook computer, a mobile phone, and a PDA (Personal Digital Assistant) have become popular. BACKGROUND ART [0002] As secondary batteries used for power supply to these portable terminals, nickel-hydrogen secondary batteries, lithium ion secondary batteries, and the like are widely used. Portable terminals are required to have more comfortable portability, and miniaturization, thinning, light weight, and high performance have been rapidly progressed. As a result, portable terminals have been used in various places. In addition, as for the battery, the miniaturization, thinness, weight reduction, and high performance of the portable terminal are required.

For example, in a lithium ion secondary battery, it is lightweight and has a large energy density. Therefore, a conductive carbonaceous material is used as a negative electrode active material, and as a binder for adhesion of the electrode active material layer to a shape- Polymer (hereinafter sometimes referred to as " polymer binder ") is used.

The polymeric binder is required to have adhesiveness with an electrode active material, resistance to a polar solvent used as an electrolytic solution, and stability under an electrochemical environment. From such a demand characteristic, a fluoropolymer such as polyvinylidene fluoride is used. However, the fluorine-based polymer has a problem that when the electrode active material layer is formed, the conductivity is deteriorated or the adhesive strength between the current collector and the electrode active material layer is insufficient. In addition, when the fluorine-based polymer is used as a negative electrode to be a reducing condition, there is a problem that the stability is not sufficient and the cycle characteristics of the secondary battery are deteriorated.

For this reason, it has been studied to use a non-fluorine-based polymer as the polymer binder in the negative electrode. For example, Japanese Unexamined Patent Application Publication No. 11-25989 and Japanese Unexamined Patent Publication (Kokai) No. 120-140684 disclose an acrylic resin composition containing an ethylenic unsaturated acid monomer such as (meth) acrylic acid, a conjugated diene such as butadiene And an aromatic vinyl such as styrene. According to such a polymer binder, high adhesion can be obtained between the current collector and the electrode active material layer, and a battery having high cycle characteristics can be obtained. In addition, various attempts have been made to improve the properties by adding various additives to the polymer binder.

Patent Documents 3 to 5 teach the addition of an alkenyl group-containing compound to an electrolytic solution for the purpose of preventing deterioration of the electrolytic solution.

Japanese Laid-Open Patent Publication No. 11-25989 Japanese Patent Application Laid-Open No. 2010-140684 Japanese Laid-Open Patent Publication No. 2001-313072 Japanese Laid-Open Patent Publication No. 2009-93839 Japanese Patent Application Laid-Open No. 2009-152133

By using the polymer binder described in Patent Documents 1 and 2 in the electrode active material layer, it is possible to obtain a battery having high adhesion between the current collector and the electrode active material layer and high cycle characteristics. However, secondary batteries have always been required to be highly functional and have a long service life. Concretely, it is required to improve cycle characteristics, low-temperature output characteristics, and the like, and to improve the adhesion between the current collector and the electrode active material layer after charging and discharging.

However, in the polymer binders described in Patent Documents 1 and 2, the adhesion between the current collector after charging and discharging and the electrode active material layer is lowered, and the cycle characteristics of the resulting secondary battery, in particular, the cycle characteristics and the low- There has been a problem that further improvement is desired.

Accordingly, it is an object of the present invention to provide a binder composition for a secondary battery negative electrode which is excellent in adhesion between a current collector after charging and discharging and an electrode active material layer, and which can contribute to improvement of cycle characteristics and low-temperature output characteristics at high temperatures of a secondary battery The purpose.

As a result of intensive investigations to solve the above problems, the inventors of the present invention have found that by using a specific compound in combination with a polymer binder used for the negative electrode active material layer, adhesion between the current collector after charging and discharging and the electrode active material layer is improved, A secondary battery having improved cycle characteristics and low-temperature output characteristics can be obtained. Thus, the present invention has been accomplished.

That is, the gist of the present invention for solving the above problems is as follows.

(1) A binder composition for a secondary battery negative electrode containing a binder and a propargylic group-containing compound, wherein the content of the propargylic group-containing compound is 0.1 to 20 parts by mass relative to 100 parts by mass of the binder.

(2) The binder composition for a secondary battery negative electrode according to (1), wherein the propargylic group-containing compound is a monoproparboxyl group-containing compound.

(3) The binder composition for a secondary battery negative electrode according to (1) or (2), wherein the binder contains an ethylenically unsaturated carboxylic acid monomer unit.

(4) The binder composition for a secondary battery negative electrode according to any one of (1) to (3), wherein the binder has a glass transition temperature of -60 占 폚 to 40 占 폚.

(5) A secondary battery negative electrode slurry composition comprising the negative electrode active material and the binder composition for a secondary battery negative electrode according to any one of (1) to (4).

(6) The slurry composition for a secondary battery negative electrode according to (5), wherein the negative active material has a BET specific surface area of 3 to 20 m 2 / g.

(7) A negative electrode for a secondary battery having a negative electrode active material layer comprising the negative electrode binder composition for a secondary battery according to any one of (1) to (4) and a negative electrode active material on the current collector.

(8) The negative electrode for a secondary battery according to (7), wherein the negative active material has a BET specific surface area of 3 to 20 m 2 / g.

(9) The negative electrode for a secondary battery according to (7) or (8), wherein the negative electrode active material is a carbon material-based active material.

(10) A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode is the negative electrode for a secondary battery according to any one of (7) to (9).

(11) The secondary battery according to (10), wherein the electrolytic solution contains vinylene carbonate.

By using the binder used in the negative electrode active material layer and the propargylic group-containing compound in combination, adhesion between the current collector and the electrode active material layer is improved, and in particular, a secondary battery improved in high temperature cycle characteristics and low temperature output characteristics is obtained. Such a working mechanism of the present invention is not necessarily obvious. Although not being interpreted in a limited manner, the inventors of the present invention have estimated the mechanism in which the above effect appears. That is, it is considered that when the propargylic group-containing compound is mixed with the negative active material layer, the propargylic group-containing compound adsorbs on the surface of the negative active material, thereby promoting the formation of a thin layer called SEI (Solid Electrolyte Interface) .

When the surface of the negative electrode active material comes into contact with the electrolyte, in some cases, a part of the electrolytic solution in contact with the edge of the negative electrode active material is decomposed. The edge portion of such a negative electrode active material is also called an active point. The decomposition product produced at the active site swells up the electrode active material layer, and the adhesion between the current collector and the electrode active material layer is lowered. As a result, the cycle characteristics and low-temperature output characteristics of the battery are impaired.

However, by forming the SEI film with the propargylic group-containing compound as described above, the direct contact between the active site of the negative electrode active material and the electrolytic solution is reduced, and the decomposition of the electrolytic solution component is prevented. As a result, the swelling of the negative electrode active material layer is reduced to maintain the fill strength, that is, the adhesion between the current collector and the negative electrode active material layer, thereby improving the cycle characteristics and the low temperature output characteristics.

Hereinafter, (1) a binder composition for a secondary battery negative electrode, (2) a slurry composition for a secondary battery negative electrode, (3) a negative electrode for a secondary battery, and (4) a secondary battery.

(1) Secondary battery For negative electrode  Binder composition

The binder composition for a secondary battery negative electrode of the present invention contains a binder and a compound containing a propargyl group.

(bookbinder)

The binder used in the present invention is not particularly limited, and various polymer compounds conventionally used as a binder of the negative electrode active material layer such as a fluorine polymer, a diene polymer, and a nitrile polymer are used. Among these, a polymer compound which is easily synthesized in an aqueous system and is easily obtained in the form of an aqueous latex is preferable. Examples of such a polymer compound include a polymer compound containing an ethylenic unsaturated acid monomer unit, preferably an ethylenic unsaturated carboxylic acid monomer unit.

The polymer compound containing an ethylenically unsaturated carboxylic acid monomer unit preferably contains an aliphatic conjugated diene monomer unit as a comonomer and may contain a unit derived from another monomer capable of copolymerizing with the monomer . From the viewpoints of durability, flexibility and adhesiveness of the binder, it is particularly preferable that these monomer units are contained in a specific ratio.

Accordingly, the binder which is particularly preferably used in the present invention is composed of an ethylenically unsaturated carboxylic acid monomer unit, an aliphatic conjugated diene monomer unit, and other monomer units copolymerizable therewith, and each monomer unit is contained at a specific ratio desirable. The ethylenically unsaturated carboxylic acid monomer unit is a polymer repeating unit obtained by polymerizing an ethylenically unsaturated carboxylic acid monomer and the aliphatic conjugated diene monomer unit is a polymer repeating unit obtained by polymerizing an aliphatic conjugated diene monomer, Another monomer unit is a polymer repeating unit obtained by polymerizing another copolymerizable monomer.

Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid, and one or more kinds thereof may be used . Of these, acrylic acid, methacrylic acid and itaconic acid are preferable, and itaconic acid is particularly preferable because of excellent adhesiveness to the current collector. When the polymer binder is used in combination with a later-described propargylic group-containing compound, the dispersibility of the binder composition in water (hereinafter sometimes abbreviated as "water dispersion") is increased as the blending amount of the propargylic group- There may be a case where it is lowered. However, water-dispersibility is improved by introducing a unit containing a carboxylic acid into the polymer binder. In addition, especially when itaconic acid, which is a dicarboxylic acid, is introduced, the affinity between the binder and water is enhanced.

As the aliphatic conjugated diene monomer, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, Dienes, substituted and side-chain conjugated hexadiene, and the like, and one or more of them may be used. 1,3-butadiene is particularly preferred.

Examples of other monomers copolymerizable therewith include an aromatic vinyl monomer, a vinyl cyanide monomer, an unsaturated carboxylic acid alkyl ester monomer, an unsaturated monomer containing a hydroxyalkyl group, and an unsaturated carboxylic acid amide monomer. Or two or more species can be used. In particular, an aromatic vinyl-based monomer is preferable in that swelling of the electrolyte solution can be suppressed.

Examples of the aromatic vinyl monomer include styrene,? -Methylstyrene, vinyltoluene, and divinylbenzene, and one or more of them may be used. Of these, styrene is particularly preferable in that swelling of the electrolyte solution can be suppressed.

Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile,? -Chlor acrylonitrile,? -Ethyl acrylonitrile, and the like, and one or more of them can be used. Particularly, acrylonitrile and methacrylonitrile are preferable.

Examples of the unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate Diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate, and one or more of them may be used. Methyl methacrylate is particularly preferred.

Examples of the unsaturated monomer containing a hydroxyalkyl group include? -Hydroxyethyl acrylate,? -Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl Hydroxyethyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis Ethyl) maleate, and 2-hydroxyethyl methyl fumarate, and they may be used alone or in combination of two or more. Especially,? -Hydroxyethyl acrylate is preferable.

Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide and N, N-dimethylacrylamide. Can be used. Particularly, acrylamide and methacrylamide are preferable.

In addition to the above monomers, monomers used in conventional emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, and vinylidene chloride may be used.

The proportion of each monomer unit in the binder in the present invention is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, and more preferably 1.0 to 10% by mass, of the ethylenically unsaturated carboxylic acid monomer unit %, And the amount of the aliphatic conjugated diene monomer unit is preferably 20 to 80 mass%, more preferably 25 to 70 mass%, and still more preferably 30 to 60 mass%, and the other monomer units copolymerizable therewith are preferable Is preferably 5 to 79.9 mass%, more preferably 10 to 70 mass%, and still more preferably 20 to 60 mass%.

When the ethylenically unsaturated carboxylic acid monomer unit is in the above range, the stability of the binder composition and the slurry composition is improved, and sufficient adhesion of the negative electrode active material and the current collector to the negative electrode for the secondary battery can be obtained. As a result, the durability, particularly the high-temperature cycle characteristics, of the obtained secondary battery is improved.

When the aliphatic conjugated diene monomer unit is in the above range, the flexibility of the negative electrode for the secondary battery and the adhesion of the negative electrode active material and the current collector are highly balanced. In addition, the durability, particularly the high-temperature cycle characteristics, of the obtained secondary battery is thereby improved.

When the copolymerizable other monomer units fall within the above range, the flexibility of the negative electrode for the secondary battery and the adhesion of the negative electrode active material and the current collector are highly balanced. In addition, the durability, particularly the high-temperature cycle characteristics, of the obtained secondary battery is thereby improved.

The glass transition temperature (Tg) of the binder is preferably -60 to 40 占 폚, more preferably -50 to 30 占 폚, particularly preferably -40 to 20 占 폚. When the binder has a Tg within the above range, it is preferable that the characteristics such as flexibility, binding property and winding property of the negative electrode, and adhesion of the negative electrode active material and the current collector are highly balanced.

When an aliphatic conjugated diene is used as the copolymerization monomer, the diene unit may be subjected to hydrogenation after polymerization. The method of adding hydrogen is not particularly limited, and a conventional method can be used.

(Propargylic group-containing compound)

In the binder composition for a secondary battery negative electrode of the present invention, a specific amount of a compound containing a propargyl group is contained in 100 parts by mass (in terms of solid content) of the binder. According to the binder composition for a secondary battery negative electrode of the present invention, by containing a specific amount of the compound containing a propargyl group, the propargylic group-containing compound can form an active site of the negative electrode active material when contacted with the negative active material, It is believed that the SEI film is formed in the vicinity. Since the SEI coating prevents the component of the electrolyte from contacting the active point, decomposition of the electrolyte solution in the cell is suppressed. As a result, an increase in electrolyte viscosity due to decomposition of the electrolyte and an increase in internal resistance of the secondary battery are suppressed, so that the high temperature storage characteristics, high temperature cycle characteristics, and low temperature output characteristics of the secondary battery are improved. In addition, swelling of the negative electrode active material layer due to the decomposition product of the electrolytic solution component is prevented, the peel strength is maintained, and the high temperature cycle characteristics and low temperature output characteristics can be further improved.

The content of the propargylic group-containing compound in the binder composition is 0.1 to 20 parts by mass, preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass based on 100 parts by mass (in terms of solid content) of the binder. When the content of the propargylic group-containing compound is too small, the formation of the SEI film becomes insufficient, the electrolyte component easily decomposes, and the cycle characteristics and output characteristics of the battery may be deteriorated. On the other hand, when the content of the propargylic group-containing compound is too large, the stability of the slurry prepared using the binder composition is impaired and the viscosity of the slurry tends to increase. As a result, the application of the slurry becomes difficult, the uniformity of the obtained negative electrode is lowered, and the output characteristics are lowered.

The propargylic group-containing compound used in the present invention has at least one propargyl group (HC≡C-CH ₂ -) in the molecule. The number of propargyl groups is not particularly limited. However, when the number of propargyl groups is increased, the dispersibility to water is lowered, and a uniform aqueous slurry may not be obtained. Therefore, the number of propargyl groups per molecule of the propargylic group-containing compound is preferably 2 or less, and particularly preferably 1. Therefore, in the present invention, a compound containing a monopropargyl group is particularly preferably used.

Specific examples of the propargylic group-containing compound include monopropargyl group-containing compounds such as benzenesulfonic acid propargyl, acrylic acid propargyl, methacrylic acid propargyl, and acetic acid propargyl;

And dipropargyl group-containing compounds such as dipropargyl carbonate.

When such a propargylic group-containing compound is brought into contact with a negative electrode active material as described later, it is considered that a propargylic group-containing compound is adsorbed on the surface of the negative electrode active material to form a thin layer called SEI film. In the negative electrode active material in which the SEI coating is formed, since the edge portion which is the active point is also covered by the coating, contact between the active point and the electrolytic solution component is reduced. As a result, the decomposition of the electrolytic solution component is suppressed, whereby the expansion of the negative electrode active material layer and the deterioration of the adhesion between the current collector and the negative electrode active material layer resulting therefrom are prevented, and the high temperature cycle characteristics and low temperature output characteristics of the battery are improved I think.

(Other components)

The binder composition for a secondary battery negative electrode of the present invention may contain, in addition to the binder and the compound containing a propargyl group, a dispersion medium for dispersing these components. The dispersion medium may be either water or an organic solvent, and may be a solvent which is hydrophilic in water as a dispersion medium, so long as the dispersion stability of the binder composition is not impaired. Examples of the hydrophilic solvent include methanol, ethanol, N-methylpyrrolidone and the like, and it is preferably 5 mass% or less with respect to water. The reaction solvent for preparing a binder described below may be a dispersion medium as it is or may be replaced with a solvent after preparation of the binder.

When the binder composition contains a dispersion medium, the total solid concentration of the binder and the propargylic group-containing compound is not particularly limited, but is suitably about 20 to 60% by mass.

The binder composition may contain various dispersants and the like used in the preparation of the binder. The binder composition may further contain an anti-aging agent, an antiseptic, and the like within a range that does not impair the dispersibility of the composition.

Examples of the antioxidant include an amine antioxidant, a phenol antioxidant, a quinone antioxidant, an organic phosphorus antioxidant, a sulfur antioxidant, and a phenothiazine antioxidant. Preservatives include isothiazoline compounds and pyrithione compounds. When the binder composition contains these components, the solid content concentration of these components in the composition is not particularly limited, but is preferably about 0.001 to 1% by mass.

(Method for producing a binder composition for a secondary battery negative electrode)

As a method of producing the binder composition for a secondary battery negative electrode of the present invention, there is a method in which the monomer composition containing the monomer is polymerized in an aqueous solvent to form an aqueous dispersion containing the binder (binder particles having binder force dissolved in an aqueous solvent or Dispersed solution or dispersion), and adding a specific amount of the propargylic group-containing compound and other optional components to the aqueous dispersion containing the binder. However, the method for producing the binder composition is not limited thereto. For example, the propargylic group-containing compound, the antioxidant, the preservative, or the like may be added in advance to the monomer composition, and then the polymerization may be carried out. In addition, these may be added to the binder composition during the polymerization or at any stage after polymerization.

The proportion of each monomer in the monomer composition in the step of obtaining an aqueous dispersion containing a binder is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, still more preferably 0.5 to 15% by mass, Of the aliphatic conjugated diene monomer is preferably from 20 to 80 mass%, more preferably from 25 to 70 mass%, and still more preferably from 30 to 60 mass% The amount of the monomer is preferably 5 to 79.9 mass%, more preferably 10 to 70 mass%, and still more preferably 20 to 60 mass%.

The aqueous solvent is not particularly limited as long as it can disperse the binder, and is usually selected from a dispersion medium having a boiling point at normal pressure of 80 to 350 占 폚, preferably 100 to 300 占 폚. The number in parentheses after the dispersion name shown below is the boiling point (in ° C) at normal pressure, and the fractional part is rounded or truncated. For example, ketones include diacetone alcohol (169),? -Butyrolactone (204); Examples of the alcohols include ethyl alcohol (78), isopropyl alcohol (82), normal propanol (97); As the glycols, ethylene glycol (193), propylene glycol (188), diethylene glycol (244); Examples of the glycol ethers include propylene glycol monomethyl ether (120), methyl cellosolve (124), ethyl cellosolve (136), ethylene glycol tertiary butyl ether (152), butyl cellosolve (174), ethylene glycol monopropyl ether (150), diethylene glycol monobutyl ether (230), triethylene glycol monobutyl ether (271), dipropylene glycol monomethyl ether (188); Examples of the ethers include 1,3-dioxolane (75), 1,4-dioxolane (101), and tetrahydrofuran (66). Among them, water is most preferable from the viewpoint that there is no flammability and the dispersion of binder is easy to be easily obtained. In addition, water may be used as a main solvent and an aqueous solvent other than the above-described water may be mixed in a range in which the dispersion state of the binder can be ensured.

The polymerization method is not particularly limited, and any of solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method and the like can be used. Examples of the polymerization reaction include ionic polymerization, radical polymerization, and living radical polymerization. From the viewpoint of production efficiency, it is possible to obtain a high molecular weight material, a polymerized material in a state in which the polymer is dispersed in water as it is, and a re-dispersion treatment is not required and can be provided for production of a slurry composition for a secondary battery negative electrode. The emulsion polymerization method is most preferable.

The emulsion polymerization may be carried out by a conventional method, for example, a method described in "Experimental Chemistry Lecture" Vol. 28, (published by Maruzen Co., Ltd., Nippon Kagaku Kogyo) Water, an additive such as a dispersing agent, an emulsifying agent, a crosslinking agent, an initiator and a monomer so as to have a predetermined composition and stirring to emulsify the monomer or the like into water, and the temperature is elevated while stirring to initiate polymerization. Alternatively, the composition is emulsified and then placed in a closed container to initiate the reaction in the same manner.

The emulsifier, the dispersant, the polymerization initiator and the like are generally used in these polymerization methods, and the amount of the emulsifier, the dispersant, and the polymerization initiator may be generally used. Further, in the polymerization, it is possible to employ seed particles (seed polymerization).

The polymerization temperature and the polymerization time may be arbitrarily selected depending on the polymerization method and the kind of the polymerization initiator to be used, but usually the polymerization temperature is about 30 DEG C or higher and the polymerization time is about 0.5 to 30 hours. Additives such as amines may be used as the polymerization auxiliary. In the aqueous dispersion of the polymer particles obtained by these methods, a hydroxide of an alkali metal (Li, Na, K, Rb, Cs), ammonia, an inorganic ammonium compound (such as NH ₄ Cl), an organic amine compound (such as ethanolamine, diethylamine Etc.) is added to the aqueous solution to adjust the pH to 5 to 10, preferably 5 to 9. The pH adjustment by the alkali metal hydroxide is preferable because it improves the binding property (fill strength) between the binder composition and the current collector and the active material.

The above-mentioned binder may be a composite polymer particle composed of two or more kinds of polymers. The composite polymer particles may be obtained also by a method of polymerizing at least one kind of monomer component by a conventional method and then adding at least one other monomer component and polymerizing by a conventional method .

Examples of the polymerization initiator to be used in the polymerization include, for example, lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexa Organic peroxides such as nonyl peroxide, and azo compounds such as?,? '- azobisisobutyronitrile, and ammonium persulfate and potassium persulfate.

In the polymerization, a chain transfer agent may be added. As the chain transfer agent, alkyl mercaptan is preferable, and specifically, n-butyl mercaptan, t-butyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, , t-dodecyl mercaptan, and n-stearyl mercaptan. Among them, n-octyl mercaptan and t-dodecyl mercaptan are preferable from the viewpoint of good polymerization stability.

In addition, other chain transfer agents may be used together with the alkyl mercaptan. Examples of the chain transfer agent that may be used in combination include terpinolene, allyl alcohol, allylamine, sodalate allylsulfonate (potassium), and sodium methallylsulfonate (potassium). The amount of the chain transfer agent to be used is not particularly limited insofar as the effects of the present invention are not impaired.

The number average particle diameter of the binder in the aqueous dispersion is preferably from 50 to 500 nm, more preferably from 70 to 400 nm. When the number average particle diameter of the binder is in the above range, strength and flexibility of the obtained negative electrode are improved. The presence of the polymer particles can be easily measured by a transmission electron microscopy method, a Coulter counter method, a laser diffraction scattering method, or the like.

The binder may be a binder composed of polymer particles having a core shell structure obtained by stepwise polymerizing the monomer.

The method of adding and mixing the propargylic group-containing compound and other optional components to the aqueous dispersion containing the binder is not particularly limited. As a mixing method, for example, there can be mentioned a method using a mixing device such as a stirring type, shaking type and rotary type. In addition, there may be mentioned a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer and a meteoroid type kneader.

In addition, an additive may be added to the resulting binder composition for a secondary battery negative electrode of the present invention in order to improve the coating property or improve the charge-discharge characteristics. Examples of the additives include cellulosic polymers such as carboxymethylcellulose, methylcellulose and hydroxypropylcellulose, polyacrylates such as sodium polyacrylate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, acrylic acid-vinyl alcohol copolymer, Methacrylic acid-vinyl alcohol copolymer, maleic acid-vinyl alcohol copolymer, modified polyvinyl alcohol, polyethylene glycol, ethylene-vinyl alcohol copolymer and polyvinyl acetate part saponification. These additives may be added to the secondary battery negative electrode slurry composition of the present invention to be described later, in addition to the method of adding them to the binder composition.

(2) Secondary battery For negative electrode Slurry  Composition

The slurry composition for a secondary battery negative electrode of the present invention comprises the binder composition for a secondary battery negative electrode and a negative electrode active material. Hereinafter, a mode of using the slurry composition for a secondary battery negative electrode of the present invention as a slurry composition for a lithium ion secondary battery negative electrode will be described.

(Negative electrode active material)

The negative electrode active material used in the present invention is a substance which exchanges electrons in the negative electrode for a secondary battery.

Examples of the negative electrode active material for a lithium ion secondary battery include a carbon material-based active material and an alloy-based active material.

The carbon material-based active material refers to an active material having carbon as a main skeleton capable of intercalating lithium, specifically, a carbonaceous material and a graphite material. The carbonaceous material generally refers to a carbon material having a low graphitization (low crystallinity) obtained by subjecting a carbon precursor to heat treatment (carbonization) at a temperature of 2000 占 폚 or less and a graphite material is obtained by heat- Graphite material having high crystallinity close to graphite.

Examples of the carbonaceous material include graphite-easy carbon which easily changes the structure of carbon by heat treatment temperature or non-graphite carbon which has a structure close to that of amorphous structure typified by glass-like carbon.

Examples of graphite-easy carbon include carbon material obtained by using tar pitch obtained from petroleum or coal as a raw material, and examples thereof include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, . The MCMB is a carbon fine particle obtained by extracting and extracting mesophase spherules produced in the course of heating the pitch at about 400 ° C. The mesophase pitch carbon fiber is a mesophase pitch obtained by growing and coalescing the mesophase spheres as a raw material Lt; / RTI >

Examples of the non-graphitizable carbon include phenol resin fired bodies, polyacrylonitrile carbon fibers, pseudo isotropic carbon, furfuryl alcohol resin fired bodies (PFA), and the like.

Examples of the graphite material include natural graphite and artificial graphite. Examples of the artificial graphite include artificial graphite heat-treated at a temperature of 2800 ° C or higher, graphitized MCMB obtained by heat-treating the MCMB at a temperature of 2000 ° C or higher, graphitized mesophase pitch carbon obtained by thermally treating the mesophase pitch- Fiber and the like.

Among these carbon-based active materials, graphite materials are preferable.

The alloy-based active material used in the present invention refers to an active material having an element capable of inserting lithium into its structure and having a theoretical electric capacity per mass of 500 mAh / g or more when lithium is inserted, specifically lithium metal, lithium A single metal or an alloy thereof, and an oxide, a sulfide, a nitride, a silicide, a carbide, a phosphide, or the like thereof are used.

As the single metal and the alloy forming the lithium alloy, a compound containing a metal such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, . Among them, a single metal such as silicon (Si), tin (Sn) or lead (Pb), an alloy containing these atoms, or a compound of these metals is used.

The alloy-based active material used in the present invention may further contain at least one non-metallic element. Specifically, SiC, SiO _x C _y (hereinafter referred to as Si-OC) (0 <x? 3, 0 <y? 5), Si ₃ N ₄ , Si ₂ N ₂ O, SiO _x (0 &lt; _x &lt; 2), SnO _x (0 &lt; x? 2), LiSiO, LiSnO, and the like. Of these, SiO _x C _y capable of lithium intercalation and deintercalation at a low electric potential is preferable. For example, SiO _x C _y Can be obtained by firing a polymer material containing silicon. Among SiO _x C _y , from the balance of capacity and cycle characteristics, a range of 0.8? X? 3, 2? Y? 4 is preferably used.

Examples of the oxide, sulfide, nitride, silicide, carbide, and phosphide include oxides, sulfides, nitrides, silicides, carbides, and phosphides of elements capable of inserting lithium. Of these, oxides are particularly preferable. Specifically, a lithium-containing metal composite oxide material containing a metal element selected from the group consisting of tin oxide, manganese oxide, titanium oxide, niobium oxide, vanadium oxide, Si, Sn, Pb and Ti atoms is used. The silicon oxide may be a material such as silicon carbide (Si-O-C).

A lithium-containing metal complex oxide, lithium-titanium complex oxide represented by the adding a _{Li x Ti y M z O 4} (0.7≤x≤1.5, 1.5≤y≤2.3, 0≤z≤1.6, M is Na, K, Co , Al, Fe, Ti, Mg , Cr, Ga, Cu, Zn , and can be exemplified by Nb), in particular, _{Li 4/3 Ti 5/3} O 4, Li 1 Ti 2 O 4, Li 4/5 Ti 11 _{/ 5} O ₄ is used.

Among them, a material containing silicon (hereinafter sometimes referred to as &quot; silicon-containing material &quot;) is preferable, and among these, Si-O-C is more preferable. In this compound, it is presumed that Li is intercalated to the Si (silicon) at a high electric potential and C (carbon) at a low electric potential, and expansion and shrinkage are suppressed more than other alloy active materials.

In the present invention, a graphite material or a silicon-containing material is preferable as the negative electrode active material, and natural graphite or Si-O-C is particularly preferable. Such an active material forms an SEI film by contact with the propargylic group-containing compound, and the active site of the edge portion is easily inactivated, and the decomposition of the electrolytic solution component can be effectively prevented. Particularly, the present invention is effective for an electrode including a carbon material-based active material.

The negative electrode active material may be used alone, or two or more thereof may be used in combination. When used in combination, a combination of a graphitic material and a silicon-containing material is preferable. The mixing ratio (graphite material / silicon-containing material) is preferably 99/1 to 40/60 by weight, more preferably 95/5 to 45/55. It is preferable that the shape of the negative electrode active material is formed into a granular shape. When the shape of the particles is spherical, a higher density electrode can be formed at the time of electrode formation.

The volume average particle diameter of the negative electrode active material is appropriately selected in consideration of balance with other constituent requirements of the battery, but is usually 0.1 to 100 占 퐉, preferably 1 to 50 占 퐉, more preferably 5 to 20 占 퐉. The 50% volume cumulative diameter of the negative electrode active material is usually 1 to 50 占 퐉, preferably 15 to 30 占 퐉, from the viewpoint of improvement of battery characteristics such as initial efficiency, load characteristics and cycle characteristics. The volume average particle diameter is determined by measuring the particle size distribution by laser diffraction. The 50% volume cumulative diameter is a 50% volume average particle diameter as measured by a laser diffraction particle size distribution analyzer (SALD-3100, manufactured by Shimadzu Corporation).

The tap density of the negative electrode active material is not particularly limited, but is preferably 0.6 g / cm 3 or more.

The BET specific surface area of the negative electrode active material is preferably 3 to 20 m 2 / g, more preferably 3 to 15 m 2 / g, and particularly preferably 3 to 10 m 2 / g. When the BET specific surface area of the negative electrode active material is in the above range, active sites on the surface of the negative electrode active material are increased, so that the low temperature output characteristic of the secondary battery is excellent.

The total content of the negative electrode active material and the binder composition in the slurry composition for a secondary battery negative electrode of the present invention is preferably 10 to 90 parts by mass, more preferably 30 to 80 parts by mass based on 100 parts by mass of the slurry composition. The content (amount equivalent to solid content) of the binder composition relative to the total amount of the negative electrode active material is preferably 0.1 to 5 parts by mass, more preferably 0.5 to 2 parts by mass, based on 100 parts by mass of the total amount of the negative electrode active material. When the total content of the negative electrode active material and the binder composition in the slurry composition and the content of the binder composition are in the above ranges, the viscosity of the resulting slurry composition for a secondary battery negative electrode is optimized and the application can be carried out smoothly. The resistance is not increased, and sufficient adhesion strength is obtained. As a result, peeling of the negative electrode active material layer from the collector in the electrode plate press process can be suppressed.

(Dispersion medium)

In the present invention, it is preferable to use water as a dispersion medium of the slurry. In the present invention, as long as the dispersion stability of the binder composition is not impaired, a dispersion medium obtained by mixing a hydrophilic solvent with water may be used. Examples of the hydrophilic solvent include methanol, ethanol, N-methylpyrrolidone and the like, and it is preferably 5 mass% or less with respect to water.

(Conductive agent)

In the slurry composition for a secondary battery negative electrode of the present invention, it is preferable to contain a conductive agent. As the conductive agent, conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor grown carbon fiber and carbon nanotube can be used. By containing the conductive agent, it is possible to improve the electrical contact between the negative electrode active materials, and to improve the discharge rate characteristic when used in the secondary battery. The content of the conductive agent in the slurry composition is preferably 1 to 20 parts by mass, more preferably 1 to 10 parts by mass based on 100 parts by mass of the negative electrode active material.

(Thickener)

In the slurry composition for a secondary battery negative electrode of the present invention, it is preferable to contain a thickening agent. Examples of the thickener include cellulosic polymers such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof;

(Modified) poly (meth) acrylic acid and their ammonium salts and alkali metal salts;

(Modified) polyvinyl alcohols, copolymers of acrylic acid or acrylic acid salts with vinyl alcohol, polyvinyl alcohols such as maleic anhydride or maleic acid, or copolymers of fumaric acid and vinyl alcohol;

Polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified polyacrylic acid, starch oxide, starch phosphate, casein, various modified starches, and the like.

The blending amount of the thickener is preferably 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the negative electrode active material. When the blending amount of the thickener is in the above range, the coating property and the adhesion with the current collector are good. In the present specification, "(modified) poly" means "unmodified poly" or "modified poly", and "(meth) acrylic" means "acrylic" or "methacrylic".

The slurry composition for a secondary battery negative electrode may contain, in addition to the above components, other components such as a reinforcing material, a leveling agent, and an electrolyte additive having a function of inhibiting electrolyte decomposition, etc., and may be contained in a negative electrode for a secondary battery described later. They are not particularly limited as long as they do not affect the cell reaction.

As the reinforcing material, various inorganic and organic spherical, plate-like, film-like or fibrous fillers can be used. By using the reinforcing material, it is possible to obtain a strong and flexible negative electrode and to exhibit excellent long-term cycle characteristics. The content of the reinforcing material in the slurry composition is usually 0.01 to 20 parts by mass, preferably 1 to 10 parts by mass, based on 100 parts by mass of the negative electrode active material. By being included in the above range, high capacity and high load characteristics are exhibited.

Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorochemical surfactants, and metal surfactants. By mixing the leveling agent, it is possible to prevent the occurrence of cratering at the time of coating or to improve the smoothness of the negative electrode. The content of the leveling agent in the slurry composition is preferably 0.01 to 10 parts by mass based on 100 parts by mass of the negative electrode active material. When the leveling agent is in the above range, productivity, smoothness and battery characteristics at the time of negative electrode production are excellent. By containing the surfactant, the dispersibility of the negative electrode active material and the like in the slurry composition can be improved and the smoothness of the negative electrode can be improved.

Vinylene carbonate and the like can be used as the electrolyte additive in the slurry composition and the electrolytic solution. The content of the electrolyte additive in the slurry composition is preferably 0.01 to 10 parts by mass based on 100 parts by mass of the negative electrode active material. When the electrolyte additive is in the above range, the cycle characteristics and the high temperature characteristics are excellent. Other examples include nanoparticles such as fumed silica and fumed alumina. By mixing the nanoparticles, the tin plasticity of the slurry composition can be controlled and the leveling property of the negative electrode can be improved. The content of the nano-particles in the slurry composition is preferably 0.01 to 10 parts by mass based on 100 parts by mass of the negative electrode active material. When the nano-particles are in the above-mentioned range, the slurry stability and productivity are excellent and high battery characteristics are exhibited.

(Water-soluble polymer)

The slurry composition for a secondary battery negative electrode of the present invention may contain a water-soluble polymer in addition to the binder composition. The water-soluble polymer is preferably a water-soluble polymer comprising 20 to 60 mass% of ethylenically unsaturated carboxylic acid monomer units, 20 to 80 mass% of (meth) acrylic acid ester monomer units and 0 to 20 mass% of other monomer units copolymerizable therewith Do. By containing the water-soluble polymer in the slurry composition for a secondary battery negative electrode, the adhesion and durability of the negative electrode for a secondary battery are improved, so that the peel strength can be improved. The water-soluble polymer in the present invention means a polymer having a viscosity of 1% aqueous solution of 0.1 to 100,000 mPa.s at pH 12.

Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid, and one or more kinds thereof may be used . The proportion of these ethylenically unsaturated carboxylic acid monomer units is more preferably 25 to 55 mass%, particularly preferably 30 to 50 mass%.

Examples of the (meth) acrylic acid ester monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, Alkyl acrylate esters such as octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate and stearyl acrylate; And examples thereof include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, Methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, n-butyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, Esters. The proportion of these (meth) acrylic acid ester monomer units is more preferably 25 to 75 mass%, particularly preferably 30 to 70 mass%.

Other copolymerizable monomers include carboxylic acid ester monomers having two or more carbon-carbon double bonds such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate; Styrene monomers such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene,? -Methylstyrene, divinylbenzene; Amide monomers such as acrylamide, N-methylol acrylamide and acrylamide-2-methylpropanesulfonic acid; ?,? - unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; Olefins such as ethylene and propylene; Halogen-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; Vinylpyrrolidone, vinylpyridine, vinylimidazole, and other heterocyclic-containing vinyl compounds. Among these,?,? -Unsaturated nitrile compounds and styrene-based monomers are preferable, and?,? - unsaturated nitrile compounds are particularly preferable. The proportion of these copolymerizable monomer units is more preferably 0 to 10 mass%, particularly preferably 0 to 5 mass%.

As a method of producing a water-soluble polymer, a method of polymerizing a monomer composition containing the monomer in an aqueous solvent to obtain an aqueous dispersion polymer and alkalizing the solution at a pH of 7 to 13. [ The aqueous solvent and the polymerization method are the same as the above-described binder composition for a secondary battery negative electrode.

Examples of the method of alkalinizing with a pH of 7 to 13 include, but not particularly limited to, an aqueous solution of an alkali metal such as aqueous solution of lithium hydroxide, aqueous solution of sodium hydroxide, aqueous solution of potassium hydroxide, aqueous solution of calcium hydroxide, aqueous solution of magnesium hydroxide and alkali solution of alkaline earth metal such as aqueous ammonia, And then adding an aqueous solution.

(Production of slurry composition for secondary battery negative electrode)

The slurry composition for a secondary battery negative electrode is obtained by mixing the binder composition, the negative electrode active material, and a conductive agent to be used, if necessary.

The mixing method is not particularly limited, and examples thereof include a method using a mixing device such as stirring, shaking, and rotating. In addition, a method using a dispersion kneading apparatus such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer and a planetary kneader may be used.

(3) For secondary batteries Negative

The negative electrode for a secondary battery of the present invention comprises the binder composition and the negative electrode active material. Specifically, the negative electrode for a secondary battery is obtained by applying and drying the secondary battery negative electrode slurry composition of the present invention onto a current collector.

(Manufacturing Method of Negative Electrode for Secondary Battery)

The method for producing the negative electrode for a secondary battery of the present invention is not particularly limited, and for example, a method of forming the negative electrode active material layer by coating the slurry composition on at least one surface, preferably both surfaces, of the current collector and drying.

The method of applying the slurry composition onto the current collector is not particularly limited. For example, methods such as a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method may be used.

Examples of the drying method include a drying method by hot air, hot air, low-humidity air, vacuum drying, and irradiation with (circle) infrared rays or electron beams. The drying time is usually 5 to 30 minutes, and the drying temperature is usually 40 to 180 ° C.

It is preferable that the negative electrode for a secondary battery of the present invention has a step of applying and drying the slurry composition on a current collector and then lowering the porosity of the negative electrode active material layer by pressure treatment using a die press or a roll press . The preferred range of porosity is 5 to 30%, more preferably 7 to 20%. If the porosity is too high, the charging efficiency and the discharge efficiency are deteriorated. When the porosity is too low, it is difficult to obtain a high volume capacity, and the negative electrode active material layer tends to be peeled off from the current collector, thereby causing a problem that defects are likely to occur. When a curable polymer is used in the binder composition, curing is preferred.

The thickness of the negative electrode active material layer in the negative electrode for a secondary battery of the present invention is usually 5 to 300 占 퐉, preferably 30 to 250 占 퐉. When the thickness of the negative electrode active material layer is in the above range, both the load characteristics and the cycle characteristics show high characteristics.

In the present invention, the content ratio of the negative electrode active material in the negative electrode active material layer is preferably 85 to 99 mass%, more preferably 88 to 97 mass%. By setting the content ratio of the negative electrode active material within the above range, flexibility and tackiness can be exhibited while exhibiting high capacity.

In the present invention, the density of the negative electrode active material layer of the negative electrode for a secondary battery is preferably 1.6 to 1.9 g / cm 3, more preferably 1.65 to 1.85 g / cm 3. When the density of the negative electrode active material layer is in the above range, a high capacity battery can be obtained.

(Whole house)

The current collector used in the present invention is not particularly limited as long as it is an electrically conductive and electrochemically durable material. However, it is preferably a metallic material because it has heat resistance. Examples of the current collector include iron, copper, aluminum, nickel, Titanium, tantalum, gold, platinum, and the like. Among them, copper is particularly preferable as the collector used for the secondary battery negative electrode. The shape of the current collector is not particularly limited, but it is preferable that the current collector is in the form of a sheet having a thickness of about 0.001 to 0.5 mm. It is preferable that the current collector is subjected to a roughening treatment in advance in order to increase the bonding strength with the negative electrode active material layer. Examples of the roughening method include mechanical roughening, electrolytic roughening, and chemical roughening. In mechanical polishing, a wire brush having a polishing pad, a grindstone, an emery pad, a steel wire, or the like to which abrasive particles are fixed is used. An intermediate layer may be formed on the surface of the current collector in order to improve the bonding strength and conductivity with the negative electrode active material layer.

(4) Secondary battery

The secondary battery of the present invention is a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the negative electrode for the secondary battery.

(Positive electrode)

The positive electrode is formed by laminating a positive electrode active material layer containing a positive electrode active material and a binder composition for a positive electrode of a secondary battery on a current collector.

(Positive electrode active material)

The positive electrode active material is largely divided into an inorganic compound and an organic compound in which an active material capable of doping and dedoping lithium ions is used.

Examples of the positive electrode active material composed of an inorganic compound include transition metal oxides, transition metal sulfides, and lithium-containing composite metal oxides of lithium and a transition metal. As the transition metal, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo are used.

Examples of transition metal oxides include MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ OP ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ Among them, MnO, V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ . Examples of the transition metal sulfide include TiS ₂ , TiS ₃ , amorphous MoS ₂ , and FeS. Examples of the lithium-containing composite metal oxide include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.

Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium composite oxide of Co-Ni-Mn, lithium composite oxide of Ni- And a lithium composite oxide of Ni-Co-Al. A lithium-containing composite metal oxide having a spinel structure, lithium manganese oxide (LiMn ₂ O ₄₎ and the substituting a part of Mn with other transition metal _{Li [Mn 3/2 M 1} /2] O 4 ( where, M is Cr, Fe, Co, Ni, Cu, etc.). As the lithium-containing composite metal oxide having olivine structure, Li _x MPO ₄ (Wherein M is at least one selected from Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B and Mo, And an olivine-type lithium phosphate compound.

As the organic compound, for example, a conductive polymer such as polyacetylene or poly-p-phenylene may be used. The iron-based oxide lacking electrical conductivity may be used as an electrode active material covered with a carbon material by causing a carbon source material to exist at the time of reduction calcination. These compounds may be partially substituted with an element. The positive electrode active material for the secondary battery may be a mixture of the inorganic compound and the organic compound.

The volume average particle diameter of the positive electrode active material is usually 0.01 to 50 mu m, preferably 0.05 to 30 mu m. When the volume average particle diameter is within the above range, the amount of the positive electrode binder composition when preparing the later-described slurry composition for a positive electrode can be reduced, whereby the deterioration of the battery capacity can be suppressed, It is easy to prepare the solution with a viscosity suitable for application, and a uniform electrode can be obtained.

The content of the positive electrode active material in the positive electrode active material layer is preferably 90 to 99.9 mass%, more preferably 95 to 99 mass%. When the content of the positive electrode active material in the positive electrode is within the above range, flexibility and adhesion can be exhibited while exhibiting high capacity.

(Binder Composition for Positive Electrode of Secondary Battery)

The binder composition for the positive electrode of the secondary battery is not particularly limited, and any known binder composition may be used. For example, the number of polyolefins such as polyethylenes, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives A soft polymer such as an acrylic soft polymer, a diene soft polymer, an olefin soft polymer, and a vinyl soft polymer can be used. These may be used alone, or two or more of them may be used in combination.

The positive electrode may contain, in addition to the above components, other components such as an electrolyte additive having a function of inhibiting decomposition of the electrolyte solution described above. They are not particularly limited as long as they do not affect the cell reaction.

The current collector may be a current collector used for the negative electrode for the secondary battery, and is not particularly limited as long as it is an electrically conductive and electrochemically durable material. However, aluminum is particularly preferable for the secondary battery positive electrode.

The thickness of the positive electrode active material layer is usually 5 to 300 占 퐉, preferably 10 to 250 占 퐉. When the thickness of the positive electrode active material layer is in the above range, both the load characteristics and the energy density exhibit high characteristics.

The positive electrode can be produced in the same manner as the above-described negative electrode for a secondary battery.

(Separator)

The separator usable as the separator includes (a) a porous separator having pores, (b) a porous separator having a polymer coat layer formed on one side or both sides, or (c) an inorganic ceramic powder And a porous separator having a porous resin coat layer formed thereon. Nonlimiting examples of these include polypropylene-based, polyethylene-based, polyolefin-based or aramid-based porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or polyvinylidene fluoride hexafluoropropylene copolymer A polymer film, a separator having a coat layer, or a separator coated with a porous film layer comprising an inorganic filler and a dispersing agent for an inorganic filler.

(Electrolytic solution)

The electrolyte used in the present invention is not particularly limited, and for example, a lithium salt dissolved in a non-aqueous solvent as a supporting electrolyte may be used. The lithium salt is, for example, _{LiPF 6, LiAsF 6, LiBF 4} , LiSbF 6, LiAlCl 4, LiClO 4, CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) 2 NLi, (CF ₃ SO ₂₎ can be cited lithium salts such as _{2 NLi, (C 2 F 5} SO 2) NLi. LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li, which are particularly easy to dissolve in a solvent and exhibit a high degree of dissociation, are preferably used. These may be used alone or in combination of two or more. The amount of the supporting electrolyte is usually not less than 1% by mass, preferably not less than 5% by mass, and usually not more than 30% by mass, preferably not more than 20% by mass, based on the electrolytic solution. If the amount of the supporting electrolyte is excessively large or excessively large, the ionic conductivity is deteriorated and the charging characteristics and the discharging characteristics of the battery are deteriorated.

The solvent used for the electrolytic solution is not particularly limited as long as it dissolves the supporting electrolyte. Usually, a solvent such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate BC) and methyl ethyl carbonate (MEC); esters such as? -butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur compounds such as sulfolane and dimethylsulfoxide are used. Particularly, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate and methyl ethyl carbonate are preferable because they are easy to obtain high ionic conductivity and have a wide temperature range for use. These may be used alone or in combination of two or more. It is also possible to add an additive to the electrolytic solution. As an additive, a carbonate compound such as vinylene carbonate (VC) is preferable, and among these, vinylene carbonate is more preferable. By containing vinylene carbonate in the electrolytic solution, the propargyl-containing compound and the vinylene carbonate accelerate the decomposition on the negative electrode active material, and decomposition of the electrolytic solution itself can be suppressed. The content of the vinylene carbonate in the electrolytic solution is preferably 0.01 to 8% by volume.

Examples of the electrolytic solution other than the above include a gelated polymer electrolyte in which a polymer electrolyte such as polyethylene oxide or polyacrylonitrile is impregnated with an electrolytic solution, or an inorganic solid electrolyte such as lithium sulfide, LiI, Li ₃ N and the like.

(Manufacturing Method of Secondary Battery)

The method for producing the secondary battery of the present invention is not particularly limited. For example, the negative electrode and the positive electrode described above are superimposed with a separator interposed therebetween. The battery is wound and folded according to the shape of the battery, inserted into the battery container, and filled with an electrolyte solution. In addition, if necessary, an over-current preventing element such as an X-fund metal, a fuse, or a PTC element, a lead plate or the like may be inserted to prevent an increase in pressure inside the battery and overcharge discharge. The shape of the battery may be any of a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, and a flat type.

Example

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto. In the present embodiment, parts and% are on a mass basis unless otherwise specified. In Examples and Comparative Examples, various physical properties were evaluated as follows.

<Dispersion Stability of Slurry>

The effects of the binder composition for secondary battery negative electrode prepared in Examples and Comparative Examples on the viscosity at the time of slurry preparation were evaluated as follows.

(60 rpm, rotor No. 4) under an environment of 25 캜 in a slurry viscosity? 0 (mPa.s) before adding the binder composition and a slurry viscosity? 1 (mPa.s) , And the slurry viscosity change? 1 /? 0 × 100 (%) before and after the addition of the binder was calculated and used as a guide for evaluation of dispersion stability. The smaller this value is, the better the dispersion stability is.

&Lt; Adhesion Strength: Peel Strength of Negative Electrode Active Material Layer &gt;

The negative electrode for a secondary battery prepared in Examples and Comparative Examples was cut out into a rectangular shape having a length of 100 mm and a width of 10 mm to prepare a test piece and a cellophane tape (JIS Z 1522 2009 ), And the stress when one end of the current collector was pulled and pulled out in a vertical direction at a tensile speed of 50 mm / min (the cellophane tape was fixed to the test stand). The measurement was carried out three times, and the average value was obtained, which was regarded as the peel strength. The larger the fill strength, the larger the binding force of the negative electrode active material layer to the current collector, i.e., the greater the adhesion strength.

The adhesion strength of the negative electrode after the high temperature cycle characteristic test described later was also evaluated in the same manner as described above.

&Lt; Durability: high temperature storage property &gt;

Using the negative electrode for a lithium ion secondary battery produced in Examples and Comparative Examples, a lithium ion secondary battery of a laminate type cell was prepared and stopped for 24 hours under an environment of 25 캜. Thereafter, charging and discharging operations were carried out under the environment of 25 캜 by charging to 4.2 V by the constant current method of 0.1 C and discharging to 3.0 V, and the initial capacity C0 was measured. Further, charging and discharging operations were performed in which the battery was charged at 4.2 V under an environment of 25 캜, stored at 60 캜 for 7 days, charged to 4.2 V by a constant current method of 0.1 C, and discharged to 3.0 V, The capacity C1 after high-temperature storage was measured. The high-temperature storage characteristics were evaluated by the rate of change in capacitance indicated by? C = C1 / C0 占 100 (%). The higher the value, the better the high-temperature storage characteristics.

&Lt; Durability: High temperature cycle characteristics &gt;

Using the negative electrode for a lithium ion secondary battery produced in Examples and Comparative Examples, a lithium ion secondary battery of a laminate type cell was prepared and stopped for 24 hours under an environment of 25 캜. Thereafter, charge and discharge operations were carried out under the environment of 25 캜 by charging to 4.2 V by a constant current method of 0.1 C and discharge to 3.0 V, and the initial capacity C0 was measured. In addition, charging and discharging to a voltage of 4.2 V by a constant current method of 0.1 C at 60 캜 and discharging to 3.0 V were repeated, and the capacity C 2 after 100 cycles was measured. The high-temperature cycle characteristics were evaluated by the rate of change in capacity indicated by? C = C2 / C0 占 100 (%). The higher the value, the better the high-temperature cycle characteristics.

&Lt; Durability: Expansion ratio of plate after high-temperature cycle characteristic test &gt;

With respect to the negative electrode after the high-temperature cycle characteristic test, the expansion rate of the electrode plate was calculated from the following formula. The lower the value, the higher the durability.

[Equation 1]

Expansion ratio of electrode plate = | thickness of negative electrode active material layer before test | thickness of negative electrode active material layer after test | / thickness of negative electrode active material layer before test

<Low Temperature Output Characteristics>

A lithium ion secondary cell of a laminate type cell was fabricated using the negative electrode for a lithium ion secondary battery manufactured in Examples and Comparative Examples and after standing still for 24 hours under the environment of 25 캜, V, and discharging to 3.0 V was carried out. Thereafter, the battery was charged to a 50% charged state (SOC 50%) by a constant current method of 0.1 C under an environment of 25 캜, and a voltage V ₀ (V) was measured. Subsequently, discharge was performed at a discharge rate of 0.1 C from the voltage V ₀ (V) under an environment of -25 캜, and a voltage V ₁₀ after 10 seconds of discharge was measured. The low temperature output characteristic is ΔV = V ₀ - V ₁₀ (V). The smaller the value, the better the low temperature output characteristic.

(Example 1)

(Preparation of binder composition)

33 parts of 1,3-butadiene, 4 parts of itaconic acid, 63 parts of styrene, 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion exchanged water and 0.5 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer After sufficiently stirring, the mixture was heated to 50 DEG C to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain an aqueous dispersion containing the binder. The glass transition temperature of the binder was 10 占 폚.

To the aqueous dispersion containing the binder was added an aqueous solution of 5% sodium hydroxide to adjust the pH to 8, and then the unreacted monomers were removed by distillation under reduced pressure, followed by cooling to 30 占 폚 or lower. To 100 parts of binder solid , And 3 parts of propargylic acid propargyl as a propargylic group-containing compound was added to obtain a binder composition.

(Production of slurry composition for secondary battery negative electrode)

100 parts of natural graphite (average particle diameter: 24.5 占 퐉) having a BET specific surface area of 5 m &lt; 2 &gt; / g as a negative electrode active material and 1% aqueous solution of carboxymethyl cellulose (MAC350HC manufactured by Nippon Seishi Chemical Co., Ltd.) One part was added in an amount corresponding to the solid content, and the solid content concentration was adjusted to 55% with ion-exchanged water, followed by mixing at 25 DEG C for 60 minutes. Next, the mixture was adjusted to a solid content concentration of 52% with ion-exchanged water, and further mixed at 25 DEG C for 15 minutes to obtain a mixed solution.

One part (based on solid content) of the binder and ion-exchanged water were added to the mixed solution to adjust the final solid content concentration to 42% and further mixed for 10 minutes. This was degassed under reduced pressure to obtain a slurry composition for a secondary battery negative electrode having good flowability. The dispersion stability of the slurry was evaluated as described above.

(Manufacture of Battery)

The secondary battery negative electrode slurry composition was coated on a copper foil having a thickness of 20 mu m with a comma coater so as to have a thickness of about 150 mu m after drying and heat treated at 60 DEG C for 1 minute and then at 120 DEG C for 1 minute, I got a disk. This electrode master was rolled by a roll press to obtain a negative electrode for a secondary battery having a thickness of the negative electrode active material layer of 80 mu m.

As a positive electrode active material, 100 parts of LiFePO ₄ having a volume average particle diameter of 0.5 μm and an olivine crystal structure and 1% aqueous solution of carboxymethyl cellulose (CMC, "BSH-12" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (2-ethylhexyl acrylate: 78% by mass, acrylonitrile: 20% by mass, methacrylic acid: 2% by mass) having a glass transition temperature of -40 占 폚 and a number average particle diameter of 0.20 占 퐉, , 5 parts of an aqueous dispersion of a 40% aqueous dispersion of the copolymer) and ion-exchanged water to a total solid content of 40% by a planetary mixer to obtain a positive electrode To prepare a slurry for the composition layer. The secondary battery positive electrode slurry composition was coated on a copper foil having a thickness of 20 탆 with a comma coater so that the film thickness after drying was about 200 탆 and heat treatment was performed at 60 캜 for 1 minute and then at 120 캜 for 1 minute, A positive electrode for a battery was obtained.

A single-layered polypropylene separator (width 65 mm, length 500 mm, thickness 25 占 퐉, manufactured by the dry method, porosity of 55%) was cut into a circle having a diameter of 18 mm.

The obtained positive electrode for a lithium ion secondary battery was arranged so that the collector surface was in contact with the aluminum-containing sheath. A separator was disposed on the side of the positive electrode active material layer side of the positive electrode. Further, the negative electrode for a lithium ion secondary battery obtained above was placed on the separator so that the side of the negative electrode active material layer side was opposed to the separator. During this filling, the electrolyte was injected so that no air remained. Further, in order to seal the openings of the aluminum foil, a heat seal was performed at 150 DEG C to open the aluminum sheath to produce a lithium ion secondary battery. The electrolytic solution was 1.0 M LiPF ₆ (Vinylene carbonate) in an amount of 2% by volume was added to a solvent (EC / DEC = 1/2 capacity ratio).

The obtained negative electrode and secondary battery were evaluated for adhesion strength, durability and low-temperature output characteristics as described above.

(Example 2)

Benzenesulfonic acid propargyl was added in an amount of 7 parts based on 100 parts of the solid content of the binder. The results are shown in Table 1.

(Example 3)

Benzenesulfonic acid propargyl was added in an amount of 15 parts based on 100 parts of the solid content of the binder. The results are shown in Table 1.

(Example 4)

The procedure of Example 1 was repeated except that propargylic acid containing compound was replaced with propargyl acrylate instead of benzenesulfonic acid propargyl. The results are shown in Table 1.

(Example 5)

The procedure of Example 1 was repeated except that propargylic group-containing compound was replaced with methacrylic acid propargyl in place of benzenesulfonic acid propargyl. The results are shown in Table 1.

(Example 6)

The procedure of Example 1 was repeated except that methacrylic acid was used instead of itaconic acid as a comonomer at the time of preparation of the binder. The results are shown in Table 1.

(Example 7)

Except that natural graphite having a BET specific surface area of 8 m &lt; 2 &gt; / g (average particle diameter: 22 mu m) was used as the negative electrode active material in place of natural graphite having a BET specific surface area of 5 m & . The results are shown in Table 1.

(Example 8)

Except that natural graphite (average particle diameter: 15 mu m) having a BET specific surface area of 15 m &lt; 2 &gt; / g was used as the negative electrode active material in place of natural graphite having a BET specific surface area of 5 m & . The results are shown in Table 1.

(Example 9)

80 parts of natural graphite (average particle diameter: 24.5 mu m) having a BET specific surface area of 5 m &lt; 2 &gt; / g and 80 parts of a BET specific surface area of 6,5 m / g were used as the negative electrode active material, instead of natural graphite having a BET specific surface area of 5 m & Except that 20 parts of SiOC (average particle diameter: 10 mu m) / m &lt; 2 &gt; / g was used. The BET specific surface area of the negative electrode active material was 5.2 m 2 / g. The results are shown in Table 1.

(Example 10)

50 parts of natural graphite (average particle diameter: 24.5 mu m) having a BET specific surface area of 5.0 m &lt; 2 &gt; / g and 50 parts of a BET specific surface area of 6.5 Except that 50 parts of SiOC (average particle diameter: 10 mu m) / m &lt; 2 &gt; / g was used. The BET specific surface area of the negative electrode active material was 5.8 m &lt; 2 &gt; / g. The results are shown in Table 1.

(Example 11)

The procedure of Example 1 was repeated except that dipropargyl carbonate was used instead of benzenesulfonic acid propargyl as the propargylic group containing compound. The results are shown in Table 1.

(Example 12)

The procedure of Example 1 was repeated except that itaconic acid was not used as a comonomer in the preparation of the binder. The glass transition temperature of the binder was 7 占 폚. The results are shown in Table 1.

(Comparative Example 1)

The procedure of Example 1 was repeated except that the propargylic group-containing compound was not added to the binder composition. The results are shown in Table 1.

(Comparative Example 2)

The procedure of Example 10 was repeated except that the propargylic group-containing compound was not added to the binder composition. The results are shown in Table 1.

(Comparative Example 3)

Benzenesulfonic acid propargyl was added in an amount of 25 parts based on 100 parts of the solid content of the binder. The results are shown in Table 1.

(Comparative Example 4)

The procedure of Example 1 was repeated except that methyl 2-octenoate was used instead of benzenesulfonic acid propargylate. The results are shown in Table 1.

By using the propargylic group-containing compound in combination with the binder composition, adhesion between the current collector and the electrode active material layer was improved, and in particular, a secondary battery improved in cycle characteristics and low-temperature output characteristics was obtained.

On the other hand, when the propargylic group-containing compound was not compounded (Comparative Examples 1 and 2), the above effect was not shown. When the compounding amount of the propargylic group-containing compound is too large (Comparative Example 3), the slurry tends to be thickened, the uniformity of the resulting negative electrode is lowered, and the output characteristics are lowered. In addition, the above-mentioned effect did not appear even when methyl 2-octenoate having an alkenyl group more similar to propargyl group (HC≡C-CH ₂ -) was used (Comparative Example 4).

Claims (13)

A binder and a propargylic group-containing compound,
Wherein the binder contains an ethylenically unsaturated carboxylic acid monomer unit,
Wherein the content of the propargylic group-containing compound is 0.1 to 20 parts by mass relative to 100 parts by mass of the binder. The method according to claim 1,
Wherein the propargylic group-containing compound is a monopropargylic group-containing compound. The method according to claim 1,
Wherein the binder has a glass transition temperature of -60 占 폚 to 40 占 폚. A secondary battery negative electrode slurry composition comprising the negative electrode active material and the binder composition for a secondary battery negative electrode according to claim 1. 5. The method of claim 4,
Wherein the negative electrode active material has a BET specific surface area of 3 to 20 m 2 / g. A negative electrode for a secondary battery having a negative electrode active material layer comprising the negative electrode binder composition for a secondary battery according to claim 1 and a negative electrode active material on a current collector. The method according to claim 6,
Wherein the negative electrode active material has a BET specific surface area of 3 to 20 m &lt; 2 &gt; / g. 8. The method according to claim 6 or 7,
Wherein the negative electrode active material is a carbon material-based active material. A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode is the negative electrode for a secondary battery according to claim 6 or 7. A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode is the negative electrode for a secondary battery. 10. The method of claim 9,
Wherein the electrolyte contains vinylene carbonate. 11. The method of claim 10,
Wherein the electrolyte contains vinylene carbonate. delete